Bile formation is greatly influenced by hormones. The proposed research will be directed at increasing our understanding of the physiologic role of the gut hormones in bile flow, determining the part paracrine substances such as the prostaglandins and intracellular mediators such as cyclic nucleotides have in hormone stimulated bile flow and determining the canalicular or ductular locus of action of the hormones which affect bile flow. Previous studies have demonstrated that glucagon increases bile flow, bile chloride secretion and bile cyclic AMP secretion rates and that the glucagon produced choleresis is mimicked by prostaglandin F2 alpha suggesting that PGF2 alpha is a mediator of the hormones action. The proposed research will explore the interrelationships of glucagon, cyclic AMP and prostaglandin F2 alpha in vivo as well as in vitro in subcellular hepatic membrane preparations. While many hormonal and non-hormonal substances increase bile flow their physiologic role in bile formation remains undetermined. Utilizing radioimmunoassay of plasma glucagon concentrations it can be determined if glucagon is a physiologic or pharmacologic stimulant of bile flow. Severe constraints on the researcher's ability to study membrane mechanisms in bile secretion are produced by the varied types of secretory and adsorptive membranes involved in the process. The proposed research will use cell membrane separation techniques to produce relatively pure hepatic canalicular and ductular cell membranes to study hormone receptor binding, hepatic cell membrane cyclic nucleotide metabolism in response to hormones and membrane immunofluorescence to identify canalicular membrane cyclic AMP. These experiments may separate out the hormone response occurring at the canalicular membrane from that occurring at the ductular membrane and determine the exact role played by cyclic AMP in hormone stimulated bile flow. These studies will increase our knowledge of the mechanisms of bile flow, elucidate the physiologic changes in bile flow associated with ingestion of micron meal and subsequent hormone release and increase our understanding of the relative role of the canalicular membrane and bile duct mucosa in bile formation.